Stevia is a perennial plant of the Asteraceae family grown in Paraguay, South America. Its scientific name is Stevia Rebaudiana Bertoni. Stevia contains components, whose sweetness is 300 times or more than that of sucrose and is planted to be used as a natural sweetener after extracting the sweet components.
Stevioside (C38H60O18), Rebaudioside A (C44H70O23). Rebaudioside C, D and E, Dulcoside A etc. have been known as sweet components of Stevia. In the generally planted Stevia variety, Stevioside (hereinafter ST) is the major component among the aforementioned sweet components, with a contained amount of Rebaudioside A (hereinafter RA) of around 40 weight % content and that of Rebaudioside C being slightly less. But depending on the variety there are various types such as those with Rebaudioside C being the major component.
Because ST has a degree of sweetness of 300 times that of sucrose, it has been widely used in the food industry as a natural sweetener. Its sweetness is relatively similar to that of sugar, but it is known that compared to RA an unpleasant taste of bitterness remains in the mouth. Compared to this, RA has good quality of sweetness, with a degree of sweetness from 1.3 to 1.5 time that of ST, so in general a sweetener of Stevia with a high RA content ratio is desirable rather than ST. The inventors of the present invention carried out plant breeding through the repetition of selective cross fertilizations of conventional varieties, thereby obtaining only Stevia varieties with very few amounts of ST compared to RA, developing sweeteners from these varieties (see Patent Literature 1 for example).
However, among the tastes such as bitterness, astringency and smoothness to the tongue, the smooth taste is quite delicate. This delicate smoothness does not rely upon the ratio between ST and RA alone. When glucose is added to the chemical structure of the various sweet components contained in Stevia, the smooth taste is improved and a method has been developed to improve the smooth and strong tastes by structurally adding glucose to the sweet components of Stevia (Patent Literature 2 and 3).
Thus, even if the content amount is small, it is very important to analyze the unknown components contained in Stevia, in particular to grasp the components in which glucose is structurally added rather than ST, and it is extremely important to execute a careful examination of the glucose structurally added to them from a perspective of taste-quality control.
Simultaneously, as the taste quality is influenced by the sweet components included in the raw material plants themselves, it is important to grasp thoroughly the sweet components in order to develop excellent Stevia varieties and use them. From now on, raw material plant improvement of breed will probably become very popular, but it will be possible to grasp in details the results of the breed improvement by specifying diligently the sweet components contained in the plants developed.
On the other hand, the inventors of the present invention developed a method for establishing a variety for plant varieties newly developed by using genes (Patent Literature 4 and 5), but actually there were no means of specifying the raw material plants regarding the sweetener extracted and processed from these raw material plants and the products which make use of them.    [Patent Literature 1] Laid Open Patent Publication JP2002-262822 Gazette    [Patent Literature 2] Patent Publication JP1957-18779 Gazette    [Patent Literature 3] Laid Open Patent Publication JP1997-107913 Gazette    [Patent Literature 4] Laid Open Patent Publication JP2003-009878, Gazette    [Patent Literature 5] International Patent Publication of Patent Cooperation Treaty—PCT WO06/093229 Gazette